How to test an ExpressJS route and 'controller' separately

I have an Express route defined as follows (where app is my Express app):

module.exports = function(app) {
  var controller = require('../../app/controllers/experiment-schema');
  app.route('/api/experiment-schemas/random').get(controller.random);
};

In that 'controller' file, I have this method:

exports.random = function (req, res, callback) {

  ExperimentSchema.count({}, function (err, count) {

    var rand = Math.floor(Math.random() * count);

    ExperimentSchema.find({})
      .skip(rand)
      .limit(1)
      .populate('mediaPool', 'artist title label')
      .exec(function (err, schema) {

        res.json(200, schema);

        if (typeof callback === 'function') {
          callback();
        }
      });
  });
}

Here, ExperimentSchema is a Mongoose model. Since the controller method hits the database, I'm passing in a callback in my test so that I can wait for those database calls to return and verify the return value. I'm doing this based on this question.

When I go to test the route, I'm testing with supertest, actually making the HTTP call to the route. The problem is that when I do this, Express is injecting next as the third argument to my random method. Now, callback() aliases next(), and everything goes haywire. How can I test my route and my controller seperately?